In-reservoir physical processes modulate aqueous and biological methylmercury export from a seasonally anoxic reservoir

Environmental Science and Technology
By: , and 

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Abstract

Anoxic conditions within reservoirs related to thermal stratification and oxygen depletion lead to methylmercury (MeHg) production, a key process governing the uptake of mercury in aquatic food webs. Once formed within a reservoir, the timing and magnitude of the biological uptake of MeHg and the relative importance of MeHg export in water versus biological compartments remain poorly understood. We examined the relations between the reservoir stratification state, anoxia, and the concentrations and export loads of MeHg in aqueous and biological compartments at the outflow locations of two reservoirs of the Hells Canyon Complex (Snake River, Idaho-Oregon). Results show that (1) MeHg concentrations in filter-passing water, zooplankton, suspended particles, and detritus increased in response to reservoir destratification; (2) zooplankton MeHg strongly correlated with MeHg in filter-passing water during destratification; (3) reservoir anoxia appeared to be a key control on MeHg export; and (4) biological MeHg, primarily in zooplankton, accounted for only 5% of total MeHg export from the reservoirs (the remainder being aqueous compartments). These results improve our understanding of the role of biological incorporation of MeHg and the subsequent downstream release from seasonally stratified reservoirs and demonstrate that in-reservoir physical processes strongly influence MeHg incorporation at the base of the aquatic food web.

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Publication type Article
Publication Subtype Journal Article
Title In-reservoir physical processes modulate aqueous and biological methylmercury export from a seasonally anoxic reservoir
Series title Environmental Science and Technology
DOI 10.1021/acs.est.2c03958
Edition Online First
Year Published 2022
Language English
Publisher ACS Publications
Contributing office(s) Forest and Rangeland Ecosys Science Center, Idaho Water Science Center
Country United States
State Idaho, Oregon
Other Geospatial Brownlee Reservoir, Hells Canyon Reservoir, Oxbow Reservoir
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